A study is proposed in which first the accuracy and precision of T1, T2 and proton density measurements on a commercial MR scanner are determined by phantom studies, and secondly, the parameters are measured in a series of controls, i.e. 100 healthy, volunteers of all ages to obtain normative data. An additional objective of the control studies is to evaluate the parameters with respect to age, sex, and weight. The next stage involves measurements for several specific classes of neuropathology: (a) cerebral ischemia (50 patients), (b) primary cerebral neoplasms (100 patients), (c) multiple sclerosis, including astrocytoma, ependymoma, medulloblastoma, meningioma, acoustic neuroma (100 patients). The objectives are to determine (1) if the effect of cerebral ischemia on T1 or T2 can be measured, (2) if T1 or T2 relaxation is related to the histologic grade of astrocytomas, (3) if T1 or T2 are specific for cerebral tumors of any type, (4) if diffuse T1, T2 or proton density abnormalities can be detected in the white matter distinct from discrete plaques in patients with multiple sclerosis, (5) if MS plaques have one or more than one characteristic pattern of relaxation parameters.